Bioimpedance based pulse waveform sensing

ABSTRACT

An arterial pulse wave may be determined via a system that includes a pressure transducing pad configured to temporarily attach to skin of a user and to deflect outwards from the skin proportionate to pressure applied by an artery. A sensor is configured to measure outward deflection of the pressure transducing pad. A plurality of electrodes are coupled to the pressure transducing pad and configured to interface with the skin of the user when the pressure transducing pad is attached to the skin of the user. The plurality of electrodes include electrodes configured to apply a current to the skin of the user, and electrodes configured to measure a voltage differential across the skin of the user. An arterial pulse wave may be determined based on at least the measured outward deflection and the measured voltage differential.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/398,331, filed Sep. 22, 2016, the entirety of which is herebyincorporated herein by reference.

BACKGROUND

Monitoring heart rate, heart rate variability, arterial blood pressure,pulse-wave velocity, and augmentation index provides useful healthinformation. These traits can be determined non-invasively based on themorphology of an arterial pulse waveform. A pulse waveform sensor may beincorporated into a wearable device.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

An arterial pulse wave may be determined via a system that includes apressure transducing pad configured to temporarily attach to skin of auser and to deflect outwards from the skin proportionate to pressureapplied by an artery. A sensor is configured to measure outwarddeflection of the pressure transducing pad. A plurality of electrodesare coupled to the pressure transducing pad and configured to interfacewith the skin of the user when the pressure transducing pad is attachedto the skin of the user. The plurality of electrodes include electrodesconfigured to apply a current to the skin of the user, and electrodesconfigured to measure a voltage differential across the skin of theuser. An arterial pulse wave may be determined based on at least themeasured outward deflection and the measured voltage differential.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an arm of a user with example thin-strip bioimpedanceelectrodes placed at the radial artery.

FIG. 2 illustrates an arm of a user with example round bioimpedanceelectrodes placed at the radial artery.

FIG. 3 illustrates an arm of a user with example thin-strip bioimpedanceelectrodes placed across the radial and ulnar arteries.

FIG. 4A shows a wearable assembly for a pulse waveform sensor.

FIG. 4B shows a cross section of a wrist of a user wearing the pulsewaveform sensor of FIG. 4A.

FIG. 5 shows a graph of example data generated using the system of FIGS.4A-4B.

FIG. 6 shows an example method for determining an arterial pulse wave ofa user.

FIG. 7 shows an exploded view of a wearable electronic device comprisinga pulse waveform sensor.

FIG. 8 schematically shows a sensory-and-logic system usable totransduce a pressure wave from a radial artery to a non-invasive pulsesensor.

DETAILED DESCRIPTION

Continuous cardiac monitoring of healthy and unhealthy patients canprovide information related to the progression of heart disease andenable early treatment. The morphology and velocity of the pulse wave inthe arteries provide meaningful information about the cardiovascularsystem. Pressure-based sensing of the pulse wave offers a non-invasiveapproach to extracting important cardiovascular parameters, such asheart rate, augmentation index, and pulse wave velocity. Such parametersmay be utilized to determine arterial stiffness, for example.

However, current non-invasive pulse-pressure sensing techniques arefocused on expert clinicians employing a handheld instrument on asuperficial artery (e.g., radial, carotid, femoral) or a common bloodpressure cuff. While this approach can work in the clinic or lab, it maycause discomfort to the subject, and only allows for a snapshot of aperson's cardiovascular state.

Recent work has explored the use of a portable sensing device worncontinuously over an artery (e.g., the radial artery at the wrist) in asimilar fashion to a piece of clothing or jewelry (e.g., a watch). Toachieve pulse-pressure sensing in a wearable device, a physicalapparatus is needed for transducing pressure waves from an artery to anon-invasive pulse-pressure sensor. However, the artery and sensor maymove relative to one another over time, making calibration andachievement of consistent results challenging. Restricting movement ofthe sensor and/or wrist-wearable device relative to the wearer mayresult in a device that is uncomfortable to wear.

Accordingly, the inventors have recognized these and other problems anddisclose an alternate method for determining an arterial pulse waveformthat uses a bioimpedance measurement device. The bioimpedancemeasurement device may be used to extract important cardiovascularparameters, such as heart rate, augmentation index, and pulse wavevelocity, similar to using a pressure transducer. Additionally, thebioimpedance measurement device may be used in tandem with a pressuretransducer. Using both sensing approaches in tandem can provide moreinformation than using either approach alone, and the cooperative use ofboth approaches may then be utilized in extracting additional importantcardiovascular parameters.

FIG. 1 illustrates an arm of a user 100 with a plurality of electrodes101 that may be placed on the underside of the arm above an artery inorder to determine a pulse waveform of user 100 via bioimpedanceanalysis. In bioimpedance analysis, a small alternating current (AC) isinjected into the area of interest using a first pair of electrodes inorder to determine the electrical impedance of body tissue. The voltagedrop across the area of interest is then measured using a second pair ofelectrodes in order to determine the magnitude and phase of thebioimpedance. In some examples, a single pair of electrodes may performboth functions. For any cross-section of tissue, the bioimpedance isdominated by the fluid filled parts of the tissue. For this reason,bioimpedance is well suited for measuring properties of blood vessels.

In this example, four electrodes (105, 110, 115, & 120) are shown.However, in some examples fewer (e.g., 2) electrodes may be used, and insome examples more (e.g., 6) electrodes may be used. In 4-wirebioimpedance approaches, the outer two electrodes carry the currentwhile the inner two electrodes measure the voltage in the area ofinterest. As such, outer electrodes 105 and 120 may be current-carryingelectrodes, while inner electrodes 110 and 115 may be voltage measuringelectrodes. Electrodes 105, 110, 115, and 120 may be placed on the skinof user 100 at the underside of the wrist between the radius 125 andflexor carpi radialis tendon 130 and thus may be situated above arteriallumen 135 where the radial artery is closest to the surface of the skin.In some examples, the electrodes may be self-adhering or may be securedin place with a temporary adhesive. In some examples, the electrodes maybe included in a wearable assembly, such as a device with a wrist-watchor cuff type form. While most examples herein are described with regardsto the radial artery, configurations where the electrodes are placed onthe underside of the wrist at the ulnar artery are also possible.

Typically, bioimpedance measurements are done on relatively large areasof the body in order to obtain a constant current flux across the skin.As such, bioimpedance measurements performed on the arm typically spacethe electrodes across the majority of the forearm. However, to the firstorder, an increase in the volume or cross section of a blood vessel ismanifest in a decrease in the local bioimpedance, as the increasedvolume of blood within the vessel makes the tissue being probed moreconductive than the surrounding tissue. The total change in blood volumeis relatively small, and thus the changes in bioimpedance are relativelysmall. This necessitates placing the electrodes such that the volumebeing sensed includes the blood vessel(s), but only includes a minimalamount of the surrounding tissue. In this way, changes in bioimpedancedue to changes in blood volume may be isolated from noise generated bytotal tissue bioimpedance.

In the configuration shown in FIG. 1, wherein the electrodes are thinstrips placed parallel to each other, but perpendicular to the radialartery, the bioimpedance is measured only at the radial artery, thuskeeping signal quality high. With a tighter spacing across the forearm,the current injected by electrodes 105 and 120 does not penetrate thetissue as much as it would were the electrodes spaced further apartacross the forearm. In this way, the percentage of the measuredbioimpedance signal that is a function of blood volume within theunderlying artery is increased. As such, bioimpedance analysis of acurrent applied directly to the radial artery yields a pulse waveformsignal that is very similar to a pulse-pressure waveform measured usinga tonometer or pressure sensor pressed into the radial artery.

Other electrode types and configurations may be used in determiningpulse waveforms via bioimpedance measurements at an artery of a user.FIG. 2 illustrates an arm of a user 200 with a plurality of electrodes201 that may be placed on the underside of the arm above an artery inorder to determine a pulse waveform of user 200 via bioimpedanceanalysis. Electrodes 201 include 4 round electrodes (205, 210, 215, &220) arranged in a four-corner pattern. Outer electrodes 205 and 220 maybe current-carrying electrodes, while inner electrodes 210 and 215 maybe voltage measuring electrodes, though other configurations arepossible. Electrodes 205, 210, 215, and 220 may be placed on the skin ofuser 200 at the underside of the wrist between the radius 225 and flexorcarpi radialis tendon 230 and thus may be situated above radial arteriallumen 235. However, in other examples, electrodes 205, 210, 215, and 220may be situated above the ulnar arterial lumen.

FIG. 3 illustrates an arm of a user 300 with a plurality of electrodes301 that may be placed on the underside of the arm above an artery inorder to determine a pulse waveform of user 300 via bioimpedanceanalysis. Electrodes 301 include 6 thin-strip electrodes (305, 310 a,310 b, 315 a, 315 b, & 320) arranged in parallel to each other, butperpendicular to the radial and ulnar arteries. Outer electrodes 305 and320 may be current-carrying electrodes, while inner electrodes 310 a,310 b, 315 a, and 315 b may be voltage measuring electrodes, thoughother configurations are possible. In this example, electrodes 305 and320 are placed on the skin of user 300 at the underside of the wrist,extending from the radius 325 to ulna 330 across flexor carpi radialistendon 335, and thus may be situated above both radial arterial lumen340 and ulnar arterial lumen 345. Electrodes 310 a and 315 a may beplaced on the skin of user 300 at the underside of the wrist between theradius 325 and flexor carpi radialis tendon 330 and thus may be situatedabove radial arterial lumen 340. Electrodes 310 b and 315 b may beplaced on the skin of user 300 at the underside of the wrist between theulna 335 and flexor carpi radialis tendon 330 and thus may be situatedabove ulnar arterial lumen 345.

Several different electrode materials may be used, such as metal (e.g.,silver chloride), conductive-gel, conductive hydrogel, metal-dopedrubber, metal-doped polymer, carbon-doped rubber, and carbon-dopedpolymer. The electrodes may be coupled to metallic electrode interfaceswhich may facilitate the injection of current and the measurement ofvoltage.

Sensing logic and/or other hardware may be specifically tuned formeasuring the radial and/or ulnar pulse wave. For example, the frequencyof the injected current affects both the signal amplitude as well as theimpedance between the skin and electrodes. Both frequency and current ofthe excitation signal may be chosen to balance signal quality and powerconsumption, while keeping well within safety and regulatory limits.Excitation frequencies may be used ranging from tens of kHz to severalhundred kHz. One implementation uses 100 kHz, though slightly higherfrequencies may yield a higher fidelity signal. One excitation currentimplementation uses about 650 μA_(RMS), though larger currents may beused up to the safety/regulatory limits indicated for a particularexcitation frequency. Smaller currents may also be used, though this mayresult in a reduced signal amplitude.

In addition to using bioimpedance analysis to measure the pulse wave atthe radial artery, a pulse waveform detection device may combine thebioimpedance sensor with a pressure sensor. In some examples, bothsensors are placed at the radial (or ulnar) artery, however, in otherexamples one sensor may be placed at the radial artery while the othersensor may be placed at the ulnar artery.

As one example, a piezo-resistive sensor may be used to measurepulse-pressure, though other sensor types are also possible. Thepressure sensor may comprise a pad placed between the skin and thesensor to help transduce radial pressure signals. In one example, aplurality of bioimpedance electrodes are integrated into the samepressure pad used to transduce the arterial pressure so that both thebioimpedance and pressure may sense the exact same region of the artery.Using this hardware setup, pulse-pressure waves and pulse-bioimpedancewaves may be measured simultaneously. When extracting cardiovascularparameters, both the pressure and bioimpedance waveforms can be used toprovide more information than is available in either one independently.

FIG. 4A shows a wearable system 400 for a pulse waveform sensor.Wearable system 400 includes a satellite housing 405 wherein a pulsewaveform sensor assembly may be housed. Satellite housing 405 is coupledto strap 410, which may be used to secure the wearable assembly around awrist of a user. Satellite housing 405 includes a pressure transducingpad 415 that may be temporarily attachable to skin of a user, and may beconfigured to interface with the skin of a user when wearable system iscoupled to the wrist of the user. Wearable assembly 400 may includefastening componentry (not shown) to temporarily couple wearableassembly 400 to a wrist of the user, the fastening componentryconfigured to couple pressure transducing pad 415 in place at an artery,such as the radial or ulnar artery.

Pressure transducing pad 415 includes a plurality of electrodes 420which may be used to measure bioimpedance of a user wearing wearableassembly 400. For example, a plurality of electrodes 420 may be coupledto an interfacing side 421 of pressure transducing pad 415 andconfigured to contact the skin of the user when interfacing side 421 ofpressure transducing pad 415 is interfacing with the skin of the user.Plurality of electrodes 420 may protrude outward from the interfacingside of the pressure transducing pad.

Interfacing side 421 of pressure transducing pad 415 may be configuredto deflect outwards from the skin proportionate to pressure applied byan artery. As such, the pressure transducing pad may be considered to bea flexible pad. In some examples, pressure transducing pad 415 maycontain and/or be coupled to a pressure transducing medium to whichpressure is applied proportionate to deflection of interfacing side 421.Pressure transducing pad 415 may be coupled to a pressure sensor (notshown) located within satellite housing 405, such as a piezo-electricpressure transducer. The pressure sensor may be configured to measureoutward deflection of the pressure transducing pad. As an example, thepressure sensor may be a piezo-electric pressure transducer.

Plurality of electrodes 420 may comprise two electrodes configured toapply a current to the skin of the user, and further comprise twoelectrodes configured to measure a voltage differential across the skinof the user. As shown, plurality of electrodes 420 are thin stripelectrodes arranged in parallel such that the two electrodes configuredto apply a current to the skin of the user are outside of the twoelectrodes configured to measure a voltage differential across the skinof the user. However, as shown in FIG. 2, plurality of electrodes 420may be round electrodes (e.g., arranged in a four-corner pattern). Insome examples, plurality of electrodes 420 may comprise two electrodesconfigured to both apply a current to the skin of the user and tomeasure a voltage differential across the skin of the user.

As an example, the entire area covered by plurality of electrodes 420may be less than or equal to a square with dimensions of 3 cm×3 cm. Eachelectrode may be a strip with an area less than 1 cm×2 cm. However,other dimensions and configurations may also be used.

FIG. 4B shows a cross section of wearable system 400 coupled to a wrist425 of a user. In this example, wearable system 400 further includesprimary device 430. Illustrated components of wrist 425 include skin435, radius 440, ulna 445, flexor carpi radialis tendon 450, radialartery 455, and tissue 460. Satellite housing 405 may be placed suchthat pressure transducing pad 415 depresses the skin 435 of the wearerinto tissue 460 between tendon 450 and radius 440, thus compressing thelumen of the radial artery. In this position, pressure pulse waves inthe radial artery may apply a pressure to flexible pad 415, which may bemechanically conducted to the underlying pressure transducer via apressure-transducing medium. Further, changes in fluid volume withinradial artery 455 may impact the bioimpedance of skin 435 and tissue460. These bioimpedance changes may be measured via electrodes 420 asdescribed above. As electrodes 420 are subject to the same pulsepressure waves as the interfacing side 421 of pressure transducing pad415, electrodes 420 may also deflect away from the skin in proportion tochanges in pulse pressure.

A controller may be configured to output a pulse wave of the user basedon at least a measured voltage differential and the measured deflection.As depicted in FIG. 4B, the voltage differential and the measureddeflection may both be derived from a same artery when wearable system400 is coupled to the wrist of the user. However, in some examples, thepressure transducing pad 415 is configured to extend across the radialartery and the ulnar artery when wearable system 400 is coupled to thewrist of the user (see for example electrodes 301 depicted in FIG. 3).

FIG. 5 shows a graph 500 of example data generated using the system ofFIGS. 4A-4B. Graph 500 includes plot 510 indicating bioimpedance at aradial artery over time, and further includes plot 520, indicatingpressure at the same radial artery over time. Plots 510 and 520 havebeen filtered and normalized so as to display over similar magnitudes.As shown in graph 500, the pulse pressure waves generated by thebioimpedance measurement device and the pulse pressure sensor have asimilar morphology (period, frequency response, features, etc.).However, some higher order frequency data may be derived from thebioimpedance measurements that are not available from the pulse pressuremeasurements. Further, the noise produced by motion of the user may bereduced for bioimpedance measurements as compared to pulse pressuremeasurements.

Pulse-pressure waves provide information on internal forces pushing outof the artery, while bioimpedance is first order representative of thevolume of the artery. Pressure and volume can thus provide additionalinformation on arterial compliance and stiffness, and thus give insightinto dynamic changes in cardiovascular state in addition to trackinglong-term changes in arterial health over time. In this way, a greaterunderstanding of cardiovascular function and health may be obtained thanwith either bioimpedance or pressure measurements alone.

FIG. 6 shows a method 600 for determining an arterial pulse wave of auser. For example, method 600 may be used to determine an arterial pulsewave of a user based on pulse-pressure and bioimpedance measurementsusing a wearable system, such as wearable system 400.

At 610, method 600 includes, at a first location on skin of a useradjacent to an underlying artery, applying current to the skin of theuser via one or more probe electrodes. The first location may include anarea of the interfacing side of a pressure transducing pad, and a widthof the interfacing side of the pressure pad may be less than a width ofan arterial lumen of the user. Applying current to the skin of the usermay include applying AC current to the skin of the user via one or moreprobe electrodes.

At 620, method 600 includes receiving, via one or more measurementelectrodes positioned at the first location, a voltage differentialacross the skin of the user. At 630, method 600 includes receiving, viaone or more pressure sensors physically coupled to the first location,deflection measurements indicative of pressure applied by the arterythrough the skin of the user. The one or more pressure sensors may bephysically coupled to the first location via a pressure transducing pad,and the one or more probe electrodes and one or more measurementelectrodes may protrude outwards from an interfacing side of thepressure transducing pad.

At 640, method 600 includes determining a pulse waveform of the userbased on at least the voltage differential and the deflectionmeasurements. In some examples, method 600 may further includeindicating arterial compliance and/or stiffness of the artery based onat least the voltage differential and the deflection measurements.

FIG. 7 shows aspects of an example sensor-and-logic system in the formof a wearable electronic device 710. The wearable electronic device 710may be configured to measure, analyze, and/or report one or morehealth/fitness parameters of a wearer of wearable electronic device 710.Wearable electronic device 710 is not limiting. One or more of thefeatures described below with reference to wearable electronic device710 may be implemented in another sensor-and-logic system, whichoptionally may have a form factor that differs from wearable electronicdevice 710.

Wearable electronic device 710 is shown disassembled in order to depictinner componentry. The illustrated device is band-shaped and may be wornaround a wrist. Wearable electronic device 710 includes a primary device712 and a satellite device 714. Components of primary device 712 andsatellite device 714 are indicated by dashed outlines. Primary device712 may have a form function similar to the main body of a watch, andmay comprise the primary user interface componentry (e.g., display,inputs, etc.) for wearable electronic device 710. Satellite device 714may comprise pulse waveform detection componentry that may enablewearable electronic device 710 to function as a wearable cardiovascularmonitoring device. The accuracy of pulse waveform detection may bedependent on the placement of the detection componentry relative to thewearer's skin and underlying tissue and vasculature. For example,including the pulse waveform detection componentry in satellite device714 may enable pulse waveform detection at the underside of the wearer'swrist while primary device 712 is situated on the back of the wearer'swrist in a position that is familiar to watch-wearers. In thisconfiguration, satellite device 714 and its internal components,including a pressure transducer assembly and a bioimpedance measurementassembly may be the functional equivalent of satellite housing 405described with reference to FIGS. 4A-4B, while primary device 712 may bethe functional equivalent of primary device 430 described with referenceto FIG. 4B.

Wearable electronic device 710 is shown having a first strap 716 and asecond strap 717. However, in some examples a single strap may beincluded, and in some examples, more than two straps may be included.The straps of wearable electronic device 710 may be elastomeric in someexamples, and one or more of the straps optionally may be comprised of aconductive elastomer. First strap 716 may be connected to primary device712 at first end 718, while second end 719 is located on the opposite,distal end of first strap 716. Similarly, second strap 717 may beconnected to primary device 712 at first end 720, while second end 721is located on the opposite, distal end of second strap 717. First strap716 comprises primary fastening componentry 722 located towards secondend 719, while second strap 717 comprises secondary fasteningcomponentry 723 located towards second end 721. The straps and fasteningcomponentry enable wearable electronic device 710 to be closed into aloop and to be worn on a wearer's wrist.

In this example, first strap 716 comprises a proximal portion 724 whichconnects to primary device 712 and a distal portion 725 that comprisesprimary fastening componentry 722. Proximal portion 724 and distalportion 725 may be coupled together via tertiary fastening componentry726. In this way the distance between primary device 712 and primaryfastening componentry 722 may be adjusted. However, in other examples,first strap 716 may be a single continuous strap that both connects toprimary device 712 and comprises primary fastening componentry 722.

Satellite device 714 may be attached to first strap 716 at a fixedposition within attachment region 727 of first strap 716, thusestablishing a fixed distance between primary device 712 and satellitedevice 714. Primary fastening componentry 722 and secondary fasteningcomponentry 723 are complementary, and thus may be adjustably engaged toadjust the circumference of wearable electronic device 710 withoutmoving the fixed position of satellite device 714 relative to primarydevice 712. In this example, primary fastening componentry 722 includesdiscrete locations for engaging with secondary fastening componentry723. However, in other examples, primary fastening componentry 722 andsecondary fastening componentry 723 may be adjustably engaged along acontinuous region.

Wearable electronic device 710 comprises a user-adjacent side 728 and anexternally-facing side 729. As such, primary device 712, satellitedevice 714, first strap 716, and second strap 717 may each have auser-adjacent side and externally facing side. In the closedconformation, wearable electronic device 710 thus comprises an innersurface (user-adjacent) and an outer surface (externally facing).

Wearable electronic device 710 includes various functional componentsintegrated into primary device 712. In particular, primary device 712includes a compute system 732, display 734, communication suite 736, andvarious sensors. These components draw power from one or moreenergy-storage cells 739. A battery—e.g., a lithium ion battery—is onetype of energy-storage cell suitable for this purpose. Examples ofalternative energy-storage cells include super- and ultra-capacitors. Inwearable electronic devices worn on the wearer's wrist, theenergy-storage cells may be curved to fit the wrist.

In general, energy-storage cells 739 may be replaceable and/orrechargeable. In some examples, recharge power may be provided through auniversal serial bus (USB) port, which may include a magnetic latch toreleasably secure a complementary USB connector. In other examples, theenergy-storage cells 739 may be recharged by wireless inductive orambient-light charging. In still other examples, the wearable electronicdevice 710 may include electro-mechanical componentry to recharge theenergy-storage cells 739 from the wearer's adventitious or purposefulbody motion. For example, batteries or capacitors may be charged via anelectromechanical generator integrated into wearable electronic device710. The generator may be turned by a mechanical armature that turnswhile the wearer is moving and wearing wearable electronic device 710.

Within primary device 712, compute system 732 is situated below display734 and operatively coupled to display 734, along with communicationsuite 736, and various sensors. The compute system 732 includes adata-storage machine 737 to hold data and instructions, and a logicmachine 738 to execute the instructions. Aspects of compute system 732are described in further detail with reference to FIG. 8. Thesecomponents may be situated within primary device 712 between top devicehousing frame 740 and bottom device housing frame 742. Primary device712 may further comprise other actuators that may be utilized tocommunicate with the wearer, such as haptic motor 744, and/or aloudspeaker (not shown).

Display 734 may be any suitable type of display. In some configurations,a thin, low-power light emitting diode (LED) array or a liquid-crystaldisplay (LCD) array may be used. An LCD array may be backlit in someimplementations. In other implementations, a reflective LCD array (e.g.,a liquid crystal on silicon, (LCOS) array) may be frontlit via ambientlight. A curved display may also be used. Further, active-matrix organiclight-emitting diode (AMOLED) displays or quantum dot displays may beused.

Communication suite 736 may include any appropriate wired or wirelesscommunication componentry. In some examples, the communication suite 736may include a USB port, which may be used for exchanging data betweenwearable electronic device 710 and other computer systems, as well asproviding recharge power. The communication suite 736 may furtherinclude two-way Bluetooth, Wi-Fi, cellular, near-field communicationand/or other radios. In some implementations, communication suite 736may include an additional transceiver for optical (e.g., infrared)communication.

In wearable electronic device 710, a touch-screen sensor may be coupledto display 734 and configured to receive touch input from the wearer.The touch-screen sensor may be resistive, capacitive, or opticallybased. Pushbutton sensors may be used to detect the state of push button748, which may include rockers. Input from the pushbutton sensor may beused to enact a home-key or on-off feature, control audio volume, turn amicrophone on or off, etc.

Wearable electronic device 710 may include a plurality of additionalsensors. Such sensors may include one or more microphones, visible-lightsensors, ultraviolet sensors, and/or ambient temperature sensors. Amicrophone may provide input to compute system 732 that may be used tomeasure the ambient sound level or receive voice commands from thewearer. Input from the visible-light sensor, ultraviolet sensor, andambient temperature sensor may be used to assess aspects of the wearer'senvironment—i.e., the temperature, overall lighting level, and whetherthe wearer is indoors or outdoors.

A secondary compute system 750 is located within satellite device 714.Secondary compute system 750 may include a data-storage machine 751 tohold data and instructions, and a logic machine 752 to execute theinstructions. Secondary compute system 750 may be situated between topsatellite housing frame 754 and bottom satellite housing frame 755. Topsatellite housing frame 754 and bottom satellite housing frame 755 maybe configured to couple satellite device 714 to a fixed position withinattachment region 727 on first strap 716 through the use of screws,bolts, clamps, etc. Top satellite housing frame 754 and bottom satellitehousing frame 755 are shown as separate components, but in someexamples, they may be coupled together by a hinge on one end, allowingsatellite device 714 to be latched together around first strap 716 atthe other end.

Secondary compute system 750 may be communicatively coupled to computesystem 732. Satellite device 714 may mediate communication betweensecondary compute system 750 and compute system 732. For example,satellite device 714 may include one or more conductive contactsconfigured to physically intersect with one or more conductive wiresextending from primary device 712 through attachment region 727 withinfirst strap 716. In other examples, secondary compute system 750 may becoupled to compute system 732 via capacitive contact between one or moreconductive contacts on satellite device 714 and one or more conductivewires within first strap 716. In other examples, a ribbon cable mayextend from primary device 712 through first strap 716 such that one ormore contacts on satellite device 714 can intersect with the ribboncable when the satellite device 714 is affixed to first strap 716. Insome examples, secondary compute system 750 may communicate with computesystem 732 via wireless communication. In some examples, satellitedevice 714 may include one or more energy-storage cells. In otherexamples, satellite device 714 and components housed therein may drawpower from energy-storage cells 739.

A bioimpedance measurement device 758 is located within satellite device714. When placed above the wearer's radial artery, the bioimpedancemeasurement device 758 may determine a voltage differential present atthe radial artery. Bioimpedance measurement device 758 may comprise aplurality of electrodes configured to interface with the skin of a user,including electrodes configured to apply a current to the skin of theuser, and electrodes configured to measure a voltage differential acrossthe skin of the user.

The determined voltage differential over time may then be converted intopulse waveform signals and utilized to determine the wearer's heartrate, blood pressure, and other cardiovascular properties. In someexamples, a pulse pressure device (not shown) may be located withinsatellite device 714 in addition to bioimpedance measurement device 758.Attachment region 727 may comprise a plurality of possible sensinglocations, each possible sensing location having a different effectivedistance from primary device 712 along the first strap 716. In someexamples, attachment region 727 may comprise a plurality of continuouspossible sensing locations, while in other examples attachment region727 may comprise a plurality of discrete possible sensing locations. Byadjusting the distance between primary device 712 and satellite device714, satellite device 714 and bioimpedance measurement device 758 may beplaced directly over the wearer's radial artery while primary device 712is positioned on the back of the wearer's wrist. In some examples,satellite device 714 may be coupled to first strap 716 at a fixedposition (e.g., at second end 719). In such examples, the distancebetween satellite device 714 and primary device 712 may be adjusted viainteractions between satellite device 714 and first strap 716, viainteractions between first strap 716 and primary device 712, and/orbetween regions of first strap 716.

Bottom satellite housing frame 755 is shown with an opening throughwhich bioimpedance measurement device 758 can establish contact with thewearer's wrist at the radial artery. However, in some examples,electrodes of bioimpedance measurement device may be situated on anexternal surface of bottom satellite housing frame 755. Wearableelectronic device 710 may be configured to instruct the wearer to adjustthe position of satellite device 714 relative to the radial artery if asignal quality of the measured bioimpedance is below a threshold. Insome examples, wearable electronic device 710 may be configured toself-adjust the position of satellite device 714 and/or the overallcircumference of wearable electronic device 710.

In some examples, bioimpedance measurement device 758 may be housed andconfigured to interface with a wearer's wrist independently from primarydevice 712. For example, bioimpedance measurement device 758 may be wornon one wrist, while primary device 712 may be worn on the other wrist.In other examples, bioimpedance measurement device 758 may be configuredto be worn while primary device 712 is not worn. Bioimpedancemeasurement device 758 may thus be configured to communicate with one ormore additional computing devices, (e.g., via secondary compute system750) such as a personal computer, tablet computer, smart phone, smartwatch, gaming device, etc. The bioimpedance measurement electronics maybe housed either internal to or external to the bioimpedance measurementdevice 758. For example, bioimpedance measurement electronics may behoused within primary device 712, while bioimpedance electrodes arehoused within satellite device 714.

FIG. 7 shows a pair of contact sensor modules 760 and 761 situated ontop device housing frame 740, which may be touchable by a wearer usingfingers on the hand opposite the wrist where wearable electronic device710 is worn. In some examples, other contact sensor modules may beincluded in addition to or as an alternative to contact sensor modules760 and 761. As one example, other contact modules may be attached touser-adjacent side 728 of primary device 712, first strap 716 and/orsecond strap 717, and thus be held in contact with points on thewearer's wrist when wearable electronic device 710 is worn. As anotherexample, one or more contact modules may be situated at or nearsecondary fastening componentry 723 on the externally-facing side 729 ofwearable electronic device 710 when wearable electronic device 710 isclosed into a loop, thus allowing the wearer to contact a point on theirbody reachable with the underside of the wearer's wrist. Additionally oralternatively, one or more contact modules may be situated on theexternally-facing side 729 of the loop at first strap 716 and/or secondstrap 717.

Contact sensor modules 760 and 761 may include independent orcooperating sensor elements, to provide a plurality of sensoryfunctions. For example, contact sensor modules 760 and 761 may providean electrical resistance and/or capacitance sensory function, whichmeasures the electrical resistance and/or capacitance of the wearer'sskin. Compute system 732 may use such input to assess whether or not thedevice is being worn, for instance. In some implementations, the sensoryfunction may be used to determine how tightly wearable electronic device710 is being worn. In some examples, a contact sensor module may alsoprovide measurement of the wearer's skin temperature. In some examples,contacting multiple contact sensor modules may allow compute system 732to determine an electrocardiogram (EKG) of the wearer.

Wearable electronic device 710 may also include motion sensingcomponentry, such as an accelerometer, gyroscope, and magnetometer. Theaccelerometer and gyroscope may furnish acceleration data along threeorthogonal axes as well as rotational data about the three axes, for acombined six degrees of freedom. This sensory data can be used toprovide a pedometer/calorie-counting function, for example. Data fromthe accelerometer and gyroscope may be combined with geomagnetic datafrom the magnetometer to further define the inertial and rotational datain terms of geographic orientation. The wearable electronic device 710may also include a global positioning system (GPS) receiver fordetermining the wearer's geographic location and/or velocity. In someconfigurations, the antenna of the GPS receiver may be relativelyflexible and extend into straps 716 and/or 717. In some examples, datafrom the motion sensing componentry may be utilized to determine aposition of the wearable electronic device 710, contact sensor modules760 and or 761, and/or bioimpedance measurement device 758 relative topredetermined sensing locations on the body of the device wearer.

In some examples, wearable electronic device 710 may also include one ormore optical sensors paired with one or more optical sources. Theoptical sources may be configured to illuminate the skin and/or theunderlying tissue and blood vessels of the wearer, while the opticalsensors may be configured to detect illumination reflected off of theskin and/or the underlying tissue and blood vessels of the wearer. Thisoptical data may be communicated to compute system 732, where the datamay be used to determine the wearer's blood-oxygen level, pulse, bloodglucose levels, or other biometric markers with optical signatures.

Compute system 732, via the sensory functions described herein, isconfigured to acquire various forms of information about the wearer ofwearable electronic device 710. Such information must be acquired andused with utmost respect for the wearer's privacy. Accordingly, thesensory functions may be enacted subject to opt-in participation of thewearer. In implementations where personal data is collected on thedevice and transmitted to a remote system for processing, that data maybe anonymized. In other examples, personal data may be confined to thewearable electronic device, and only non-personal, summary datatransmitted to the remote system.

As evident from the foregoing description, the methods and processesdescribed herein may be tied to a sensory-and-logic system of one ormore machines. Such methods and processes may be implemented as acomputer-application program or service, an application-programminginterface (API), a library, firmware, and/or other computer-programproduct. FIG. 7 shows one, non-limiting example of a sensory-and-logicsystem to enact the methods and processes described herein. However,these methods and process may also be enacted on sensory-and-logicsystems of other configurations and form factors, as shown schematicallyin FIG. 8.

FIG. 8 schematically shows a form-agnostic sensory-and-logic system 810that includes a sensor suite 812 operatively coupled to a compute system814. The compute system includes a logic machine 816 and a data-storagemachine 818. The compute system is operatively coupled to a displaysubsystem 820, a communication subsystem 822, an input subsystem 824,and/or other components not shown in FIG. 8.

Logic machine 816 includes one or more physical devices configured toexecute instructions. The logic machine may be configured to executeinstructions that are part of one or more applications, services,programs, routines, libraries, objects, components, data structures, orother logical constructs. Such instructions may be implemented toperform a task, implement a data type, transform the state of one ormore components, achieve a technical effect, or otherwise arrive at adesired result.

Logic machine 816 may include one or more processors configured toexecute software instructions. Additionally or alternatively, the logicmachine may include one or more hardware or firmware logic machinesconfigured to execute hardware or firmware instructions. Processors ofthe logic machine may be single-core or multi-core, and the instructionsexecuted thereon may be configured for sequential, parallel, and/ordistributed processing. Individual components of a logic machineoptionally may be distributed among two or more separate devices, whichmay be remotely located and/or configured for coordinated processing.Aspects of a logic machine may be virtualized and executed by remotelyaccessible, networked computing devices in a cloud-computingconfiguration.

Data-storage machine 818 includes one or more physical devicesconfigured to hold instructions executable by logic machine 816 toimplement the methods and processes described herein. When such methodsand processes are implemented, the state of the data-storage machine maybe transformed—e.g., to hold different data. The data-storage machinemay include removable and/or built-in devices; it may include opticalmemory (e.g., CD, DVD, HD-DVD, Blu-Ray Disc, etc.), semiconductor memory(e.g., RAM, EPROM, EEPROM, etc.), and/or magnetic memory (e.g.,hard-disk drive, floppy-disk drive, tape drive, MRAM, etc.), amongothers. The data-storage machine may include volatile, nonvolatile,dynamic, static, read/write, read-only, random-access,sequential-access, location-addressable, file-addressable, and/orcontent-addressable devices.

Data-storage machine 818 includes one or more physical devices. However,aspects of the instructions described herein alternatively may bepropagated by a communication medium (e.g., an electromagnetic signal,an optical signal, etc.) that is not held by a physical device for afinite duration.

Aspects of logic machine 816 and data-storage machine 818 may beintegrated together into one or more hardware-logic components. Suchhardware-logic components may include field-programmable gate arrays(FPGAs), program- and application-specific integrated circuits(PASIC/ASICs), program- and application-specific standard products(PSSP/ASSPs), system-on-a-chip (SOC), and complex programmable logicdevices (CPLDs), for example.

Display subsystem 820 may be used to present a visual representation ofdata held by data-storage machine 818. This visual representation maytake the form of a graphical user interface (GUI). As the hereindescribed methods and processes change the data held by the storagemachine, and thus transform the state of the storage machine, the stateof display subsystem 820 may likewise be transformed to visuallyrepresent changes in the underlying data. Display subsystem 820 mayinclude one or more display subsystem devices utilizing virtually anytype of technology. Such display subsystem devices may be combined withlogic machine 816 and/or data-storage machine 818 in a shared enclosure,or such display subsystem devices may be peripheral display subsystemdevices. Display 734 of FIG. 7 is an example of display subsystem 820.

Communication subsystem 822 may be configured to communicatively couplecompute system 814 to one or more other computing devices. Thecommunication subsystem may include wired and/or wireless communicationdevices compatible with one or more different communication protocols.As non-limiting examples, the communication subsystem may be configuredfor communication via a wireless telephone network, a local- orwide-area network, and/or the Internet. Communication suite 736 of FIG.7 is an example of communication subsystem 822.

Input subsystem 824 may comprise or interface with one or moreuser-input devices such as a keyboard, touch screen, button, dial,joystick, or switch. In some embodiments, the input subsystem maycomprise or interface with selected natural user input (NUI)componentry. Such componentry may be integrated or peripheral, and thetransduction and/or processing of input actions may be handled on- oroff-board. Example NUI componentry may include a microphone for speechand/or voice recognition; an infrared, color, stereoscopic, and/or depthcamera for machine vision and/or gesture recognition; a head tracker,eye tracker, accelerometer, and/or gyroscope for motion detection and/orintent recognition. Push button 748 of FIG. 7 is an example of inputsubsystem 824.

Sensor suite 812 may include one or more different sensors—e.g., pulsewaveform sensor 825, a touch-screen sensor, push-button sensor,microphone, visible-light sensor, ultraviolet sensor,ambient-temperature sensor, contact sensors, and/or GPS receiver—asdescribed above with reference to FIG. 7. Sensor suite 812 may includemotion sensor suite 826. Motion sensor suite 826 may include one or moreof an accelerometer, gyroscope, magnetometer, or other suitable motiondetectors.

As described herein, pulse waveform sensor 825 may include bioimpedancesensor 830 and/or pressure transducer 832. Compute system 814 mayinclude pulse waveform sensor control subsystem 834, which may becommunicatively coupled to logic machine 816 and data-storage machine818. Bioimpedance sensor 830 may comprise two or more sets ofelectrodes; a first set configured to inject current into the skin 836of a user, and a second set configured to transduce a voltagedifferential across the skin 836 of a user. The voltage differential maybe indicative of volume changes of the radial artery 838 of the user.Pressure transducer 832 may comprise one or more piezo-resistive sensorsconfigured to provide absolute pressure signals to compute system 814via an analog-to-digital converter. Pressure transducer 832 may beconfigured to transduce pressure waves from the radial artery 838through the skin 836 of the user.

Pulse waveform sensor control subsystem 834 may further process the rawsignals to determine heart rate, blood pressure, caloric expenditures,etc. Processed signals may be stored and output via compute system 814.Control signals sent to pulse waveform sensor 825 may be based onsignals received from bioimpedance sensor 830, pressure transducer 832,signals derived from sensor suite 812, information stored indata-storage machine 818, input received from communication subsystem822, input received from input subsystem 824, etc.

In one example, a system for determining an arterial pulse wave of auser comprises a pressure transducing pad temporarily attachable to skinof a user, the pressure transducing pad configured to deflect outwardsfrom the skin proportionate to pressure applied by an artery; a sensorconfigured to measure outward deflection of the pressure transducingpad; and a plurality of electrodes coupled to the pressure transducingpad and configured to interface with the skin of the user when thepressure transducing pad is attached to the skin of the user, theplurality of electrodes comprising electrodes configured to apply acurrent to the skin of the user, and electrodes configured to measure avoltage differential across the skin of the user. In such an example, orany other example, the plurality of electrodes may additionally oralternatively comprise two electrodes configured to apply a current tothe skin of the user, and further comprise two electrodes configured tomeasure a voltage differential across the skin of the user. In any ofthe preceding examples, or any other example, the plurality ofelectrodes may additionally or alternatively be thin strip electrodesarranged in parallel such that the two electrodes configured to apply acurrent to the skin of the user are outside of the two electrodesconfigured to measure a voltage differential across the skin of theuser. In any of the preceding examples, or any other example, theplurality of electrodes may additionally or alternatively be roundelectrodes arranged in a four-corner pattern. In any of the precedingexamples, or any other example, the plurality of electrodes mayadditionally or alternatively occupy a footprint less than or equal to 3cm×3 cm. In any of the preceding examples, or any other example, theplurality of electrodes may additionally or alternatively comprise twoelectrodes configured to both apply a current to the skin of the userand to measure a voltage differential across the skin of the user. Inany of the preceding examples, or any other example, the sensorconfigured to measure outward deflection of the pressure transducing padmay additionally or alternatively be a piezo-electric pressuretransducer. In any of the preceding examples, or any other example, thesystem may additionally or alternatively comprise a wearable assemblyincluding fastening componentry configured to couple the pressuretransducing pad in place at the artery. In any of the precedingexamples, or any other example, the artery may additionally oralternatively be a radial artery. In any of the preceding examples, orany other example, the artery may additionally or alternatively be anulnar artery. In any of the preceding examples, or any other example,the pressure transducing pad may additionally or alternatively includean interfacing side configured to contact the skin of the user, andwherein the plurality of electrodes protrude outward from theinterfacing side of the pressure transducing pad.

In another example, a method for determining an arterial pulse wave of auser comprises, at a first location on skin of a user adjacent to anunderlying artery, applying current to the skin of the user via one ormore probe electrodes; receiving, via one or more measurement electrodespositioned at the first location, a voltage differential across the skinof the user; receiving, via one or more pressure sensors physicallycoupled to the first location, deflection measurements indicative ofpressure applied by the artery through the skin of the user; determininga pulse wave of the user based on at least the voltage differential andthe deflection measurements. In such an example, or any other example,the one or more pressure sensors may additionally or alternatively bephysically coupled to the first location via a pressure transducing pad,and the one or more probe electrodes and one or more measurementelectrodes may additionally or alternatively protrude outwards from aninterfacing side of the pressure transducing pad. In any of thepreceding examples, or any other example, the first location includes anarea of the interfacing side of the pressure pad, and wherein a width ofthe interfacing side of the pressure pad is less than a width of anarterial lumen of the user. In any of the preceding examples, or anyother example, the method may additionally or alternatively compriseindicating an arterial stiffness of the artery based on at least thevoltage differential and the deflection measurements. In any of thepreceding examples, or any other example, applying current to the skinof the user via one or more probe electrodes may additionally oralternatively include applying AC current to the skin of the user viaone or more probe electrodes.

In yet another example, a wearable system for determining an arterialpulse wave of a user, comprises fastening componentry to temporarilycouple the wearable system to a wrist of the user; a plurality ofelectrodes configured to contact the skin of the user, the plurality ofelectrodes occupying a footprint less than or equal to 3 cm×3 cm, theplurality of electrodes comprising electrodes configured to apply acurrent to the skin of the user, and electrodes configured to measure avoltage differential across the skin of the user; and a controllerconfigured to output a pulse wave of the user based on at least thevoltage differential. In such an example, or any other example, theplurality of electrodes may additionally or alternatively comprise twoelectrodes configured to apply a current to the skin of the user, andmay additionally or alternatively comprise two electrodes configured tomeasure a voltage differential across the skin of the user. In any ofthe preceding examples, or any other example the plurality of electrodesmay additionally or alternatively be thin strip electrodes arranged inparallel such that the two electrodes configured to apply a current tothe skin of the user are outside of the two electrodes configured tomeasure a voltage differential across the skin of the user. In any ofthe preceding examples, or any other example the plurality of electrodesmay additionally or alternatively be round electrodes arranged in afour-corner pattern.

It will be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. As such, various acts illustrated and/ordescribed may be performed in the sequence illustrated and/or described,in other sequences, in parallel, or omitted. Likewise, the order of theabove- described processes may be changed.

The subject matter of the present disclosure includes all novel andnon-obvious combinations and sub-combinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

1. A system for determining an arterial pulse wave of a user,comprising: a pressure transducing pad temporarily attachable to skin ofa user, the pressure transducing pad configured to deflect outwards fromthe skin proportionate to pressure applied by an artery; a sensorconfigured to measure outward deflection of the pressure transducingpad; and a plurality of electrodes coupled to the pressure transducingpad and configured to interface with the skin of the user when thepressure transducing pad is attached to the skin of the user, theplurality of electrodes comprising electrodes configured to apply acurrent to the skin of the user, and electrodes configured to measure avoltage differential across the skin of the user.
 2. The system of claim1, wherein the plurality of electrodes comprise two electrodesconfigured to apply a current to the skin of the user, and furthercomprise two electrodes configured to measure a voltage differentialacross the skin of the user.
 3. The system of claim 2, wherein theplurality of electrodes are thin strip electrodes arranged in parallelsuch that the two electrodes configured to apply a current to the skinof the user are outside of the two electrodes configured to measure avoltage differential across the skin of the user.
 4. The system of claim2, wherein the plurality of electrodes are round electrodes arranged ina four-corner pattern.
 5. The system of claim 2, wherein the pluralityof electrodes occupy a footprint less than or equal to 3 cm x 3 cm. 6.The system of claim 1, wherein the plurality of electrodes comprise twoelectrodes configured to both apply a current to the skin of the userand to measure a voltage differential across the skin of the user. 7.The system of claim 1, wherein the sensor configured to measure outwarddeflection of the pressure transducing pad is a piezo-electric pressuretransducer.
 8. The system of claim 1, further comprising a wearableassembly including fastening componentry configured to couple thepressure transducing pad in place at the artery.
 9. The system of claim8, wherein the artery is a radial artery.
 10. The system of claim 8,wherein the artery is an ulnar artery.
 11. The system of claim 1,wherein the pressure transducing pad includes an interfacing sideconfigured to contact the skin of the user, and wherein the plurality ofelectrodes protrude outward from the interfacing side of the pressuretransducing pad.
 12. A method for determining an arterial pulse wave ofa user, comprising: at a first location on skin of a user adjacent to anunderlying artery, applying current to the skin of the user via one ormore probe electrodes; receiving, via one or more measurement electrodespositioned at the first location, a voltage differential across the skinof the user; receiving, via one or more pressure sensors physicallycoupled to the first location, deflection measurements indicative ofpressure applied by the artery through the skin of the user; determininga pulse wave of the user based on at least the voltage differential andthe deflection measurements.
 13. The method of claim 12, wherein the oneor more pressure sensors are physically coupled to the first locationvia a pressure transducing pad, and wherein the one or more probeelectrodes and one or more measurement electrodes protrude outwards froman interfacing side of the pressure transducing pad.
 14. The method ofclaim 13, wherein the first location includes an area of the interfacingside of the pressure pad, and wherein a width of the interfacing side ofthe pressure pad is less than a width of an arterial lumen of the user.15. The method of claim 12, further comprising: indicating an arterialstiffness of the artery based on at least the voltage differential andthe deflection measurements.
 16. The method of claim 12, whereinapplying current to the skin of the user via one or more probeelectrodes includes applying AC current to the skin of the user via oneor more probe electrodes.
 17. A wearable system for determining anarterial pulse wave of a user, comprising: fastening componentry totemporarily couple the wearable system to a wrist of the user; aplurality of electrodes configured to contact the skin of the user, theplurality of electrodes occupying a footprint less than or equal to 3cm×3 cm, the plurality of electrodes comprising electrodes configured toapply a current to the skin of the user, and electrodes configured tomeasure a voltage differential across the skin of the user; and acontroller configured to output a pulse wave of the user based on atleast the voltage differential.
 18. The wearable system of claim 17,wherein the plurality of electrodes comprise two electrodes configuredto apply a current to the skin of the user, and further comprise twoelectrodes configured to measure a voltage differential across the skinof the user.
 19. The wearable system of claim 18, wherein the pluralityof electrodes are thin strip electrodes arranged in parallel such thatthe two electrodes configured to apply a current to the skin of the userare outside of the two electrodes configured to measure a voltagedifferential across the skin of the user.
 20. The wearable system ofclaim 18, wherein the plurality of electrodes are round electrodesarranged in a four-corner pattern.